One important thing when listening to someone's speech is to remember your surroundings and the backgrounds of the various individuals.
Very similar to Analog's story of "cursing guy", my gf grew up in an environment in which "cursing" was not such a big deal. It is not uncommon for her to drop f-bombs when talking to her own mother and her mom slings them right back.
My family is very much the opposite. I used to get my mouth washed out for saying "hell" or "damn" as a child
My mother would find my girlfriend's language incredibly offensive. However, my girlfriend's mother finds it offensive that I refer to her as "m'am" or "Mrs. <insert last name>". She much prefers to be called by her first name.
Calling someone Mrs. or Mr. so and so could hardly be seen as improper languague, but in that situation it definitely is! So I have learned to refer to her by her first name. By the same token, my girlfriend has learned to restrain her diction when in the presence of my mother (as hard as it may be sometimes).
I think the key is to always be aware of your habits and those of your friends/family. A person may use the foulest language known to man in his everday life, but if he knows when to cut it off to not offend others, he is a respectful person.
Language is a matter of respect in the end and I think it does not have much to do with morality. I find morality is tied much closer to action.